Web / Traefik Interview questions

How does Traefik handle load balancing across multiple service instances?

When a service has multiple server URLs, Traefik distributes incoming requests across them using a load-balancing algorithm, with weighted round robin as the default behavior for HTTP services.

Each server can be assigned a weight to send it proportionally more or less traffic, which is the same mechanism used for canary releases, where a new version might get a 10% weight against 90% for the stable version.

Traefik also supports passive health checking through active healthCheck probes on the service, so instances that stop responding are automatically pulled out of rotation until they recover, without any manual intervention.

All of this happens at the service level, meaning the router and its rule stay completely unaware of how many backend replicas exist behind the name they point to, or how traffic is actually being split between them.

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The default HTTP load-balancing behavior in Traefik is: Random selection with no weighting

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Weighted round robin

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Least-connections only

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IP hash only, with no alternative

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How are unhealthy instances handled during load balancing? Traefik keeps sending them traffic regardless of health checks

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They are automatically pulled out of rotation until they pass health checks again

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The entire service is deleted permanently

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Traefik restarts the Docker daemon

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List the supported configuration providers in Traefik? How does Traefik handle load balancing across multiple service instances? How do you enable the Traefik dashboard? What is the purpose of Let's Encrypt integration in Traefik? What is a middleware chain in Traefik and why order it carefully? What is the difference between Host and HostRegexp rules? What is Traefik? What are routers in Traefik? What is the Traefik file provider? How do you configure Traefik using Docker labels? What are services in Traefik? What is a certificate resolver in Traefik? Why is dynamic configuration preferred over static configuration for routing rules? What is the difference between Path and PathPrefix routing rules? What are middlewares in Traefik? What are providers in Traefik? What are the main features of Traefik? What is the purpose of an entrypoint in Traefik? Define an IngressRoute in Traefik? Why would you use sticky sessions in Traefik?

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